Nepodin (CAS: 3785-24-8), also referred to as musizin and dianellidin, has a structure represented by the formula (1) given below. It is known that nepodin has pharmacological activities to improve various conditions, including glucose tolerance and blood lipid levels and to ameliorate metabolic syndromes, by activating 5′-adenosine monophosphate-activated protein kinase (AMPK) (See, for example, Non-Patent Document 1 below, the entire disclosure of which is incorporated herein by reference).

Rumex plants, perennial plants of the genus Rumex of the family Polygonaceae, are known as a natural material containing nepodin. Among known Rumex species are R. japonicus, R. crispus, R. obtusifolius and R. maritimus. 
In a known technique to obtain nepodin from Rumex plants, plant parts such as roots and stems are subjected to an extraction process using organic solvents that can dissolve nepodin, such as ethanol and ethyl acetate (See, Non-Patent Documents 1 and 2 below, the entire disclosure of which is incorporated herein by reference).